is 1868 (1996) anodic coatings on aluminium and its alloys
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IS 1~868 : 1~996
Indian Standard
ANODIC COATINGS ON ALUMINIUM AND
ITS ALLOYS
- SPECIFICATION
Third Revision)
ICS 2.5.220.30;77.120.10
0 BIS 1996
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN 9 BAHADUR SHAH ZAFAR MARC
NEW DELHI I 10002
December 1996
Price Group 3
( Reaffirmed 2006 )
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Metallic and Non-metallic Finishes Sectional Committee. MTD 20
FOREWORD
This Indian Standard (Third prevision) was adopted by the Bureau of Indian Standards, after the draft finalized
by the Metallic and Non-metallic Finishes Sectional Committee had been approved by the Metallurgical
Engineering Division Council.
This Standard was first published in 1961 and subsequently revised in 1968 and 1982. While reviewing
this standard, the committee desired to revise this standard and various clauses have been aligned with
International Standards.
In this revision following changes have been made:
a) Scope of the standard has been widened.
b) The existing clause on terminology has been revised incorporating definition of additional fifteen
terms.
c) A new clause providing general guidelines on grades of Aluminium suitable for anodizing has
been added.
d) A new clause on Surface Texture of aluminium surface prior to anodizing has also been incorporated.
No one coating can satisfy all the requirements of this standard since individually the requirements may
he incompatible with each other. A list of information which should he provided along with the inquiry
and order is given in 7. It is in particular, essential that the purchaser states the clauses which are relevant,
and specifying in each case the grade number of the agreed standard of performance desired. Merely asking
for anodizing to IS 1868 without this information is insufficient.
In the formulation of this standard, assistance has been derived from IS0 7599: 1983, Anodizing of aluminium
and its alloy-General specification for anodic oxide coatings on aluminium, issued by the International
Organization for Standardization.
For the purpose of deciding whether a particular requirements of this standard is complied with, the final
value, observed of calculated, expressing the result of a test or analysis, shall be rounded off in accordance
with IS 2 : 1960 Rules for rounding off numerical values (revised). The number of significant places retained
in the rounded off value should be the same as that of the specified value in this standard.
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Indian
ANODIC COATINGS
IS 1868 : 1996
Standard
ON ALUMINWM AND
ITS ALLOYS
- SPECIFICATION
Third Revision)
1
SCOPE
1.1
This standard lays down general specification for
anodic oxide coatings on aluminium. It defines the
characteristic properties of anodic oxide coatings on
aluminium, lists methods of test for checking the
characteristic properties, specifies minimum
performance requirements, gives information on the
grades of aluminium suitable for anodizing and
describes the importance of pretreatment to ensure
the required appearance or texture of the finished
work.
1.2 This standard does not cover hard anodized
coatings for engineering purpose, for which abrasion
and wear resistance are the primary characteristics.
2 REFERENCES
The Indian Standards listed in Annex A are necessary
adjuncts to this standard.
3 SUPPLY OF MATERIAL
The general requirements relating to the supply of
material shall be as laid down in IS 1387:1993.
4 TERMINOLOGY
For the purpose of this standard, definitions given
in IS 3554:1966 as well as the following shall apply.
4.1 Anodized Aluminium
Alumiminium with an anodic coating, produced by
an electrolytic oxidation process in which the surface
of aluminium is converted to a coating, generally an
oxide, having protective, decorative or functional
properties.
4.2
Ciear Anodized Aluminium
Aluminium with a substantially colourless, translucent
anodic oxide coating.
4.3 Colour Anodized Aluminium
Aluminium with an anodic oxide coating that is
coloured by absorptive dyes.
4.4 Integral Colour Anodizing
Anodizing of aluminium using an appropriate (usually
organic acid-based) electrolyte which produces
coloured oxide coating during the anodizing process
itself on specific aluminium
alloys.
.4.5 Electrolytic Colouring
The colouring of an anodic oxide coating by the
electrolytic deposition of metals or metal oxide in
the porous structure.
4.6 Bright Anodized Aluminium
Anodized aluminium
with a high specular reflectance
as the primary characteristic.
4.7 Protective Anodizing
Anodizing where protection against corrosion or wear
is the primary characteristics and appearance is
secondary or of no importance.
4.8
Decorative Anodizing
Anodizing where a decorative finish with a uniform
or asthetically pleasing appearance is the primary
characteristic.
4.9 Architectural Anodizing
Anodizing to produce an architectural finish to be
used in permanent, exterior and static situations where
both appearance and long life are important.
4.10 Sealing
A hydration treatment of anodic oxide coatings on
aluminium applied after anodizing to reduce porosity
and/or the absorption capacity of the coating.
4.11 Significant Surface
The part of the article covered or to be covered by
the coating and for which the coating is essential
for serviceability and/or appearance.
NOTE-When necessary the significant surface is to he agreed
upon between the manufacturer and the purchaser and is to
be indicated on the drawings or by providing smtably marked
sample.
4.12 Measuring Area
The area of the significant surface over which a single
measurement is made.
1
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IS 1868
:
1996
Measuring area for the various methods is defined
as following:
a) For analytical method - the area over
which the coating is removed;
b) For the anodic dissolution method - the
area enclosed by the sealing ring of the cell;
c) For the microsectional method - the place
at which a single measurement is made; and
d) For non-destructive methods - the probe
area or the area included in the reading.
4.13 Reference Area
The area within which a specified number of single
measurements are required to be made.
4.14 Local Thickness
The mean of the thickness measurements, of which
a specified number is made within a reference area.
4.15 Minimum Local Thickness
The lowest value of the coating thickness at any point
on the significant surface.
4.16 Maximum Local Thickness
The highest value of the coating thickness at any
~point on the significant surface.
4.17
Average Thickness
Either the value obtained by analytical methods, or
the mean value of a specified number of local thickness
measurements that are evenly distributed over the
significant surface.
4.18 Impregnation
A treatment carried out after anodizing in order to
plug the pores of the anodic oxidation coating, but
not involving hydrothermal sealing.
5 GRADES OF ALUMINIUM FOR ANODIZING
General guidance on anodising of different categories
of aluminium is given in Annex B.
6 SURFACE TEXTURE
General guidance on detailes of surface texture is
given in Annex C.
7 INFORMATION TO BE GIVEN WITH THE
INQUIRY AND ORDER
7.1 The following is a list of the characteristic
properties of anodic oxide coatings that may be
required to be specified and measured, or otherwise
agreed upon.
Only some of the properties will be significant in
any particular application. The anodizer shall be
notified of either the end use or of the specific
properties required.
Some properties (for example specular reflectance)
are only obtainable by the use of special alloys, and
some properties may be mutually incompatiable with
others.
The following information, where appropriate, should
be provided with the inquiry and order:
4
b)
c>
4
e)
0
g)
W
3
k)
7.2
Thickness (see 9)
Quality of sealing (see 10
Colour and appearance (sc~e 11
Corrosion resistance (see 12)
Abrasion resistance (see 13)
Resistance to crazing deformation (see 14)
Fastness to light (see 15)
Light reflection properties (see 16)
Electrical breakdown potential (see 17),
and
Continuity of the coating see 18)
Sampling Procedure
Sampling procedure shall he as agreed to between
the anodiser and the purchaser. For sampling plan
IS 2500 (Part 1) :I992 may be referred.
8 TEST PIECES
8.1 Wherever practicable, test pieces shall be the
production component. Howcvcr, if by agreement,
special pieces are prepared for convenience as referee
or acceptance test, they shall be made of the same
material as the production batch they represent, and
shall be anodized by the same process and at the
same time.
8.2 Acceptance Tests
Acceptance tests shall be as agreed between the
anodizer and the customer. However following
acceptance tests can be adopted by the users:
a>
b)
c>
4
Colour and appearance;
Thickness (see 9);
Quality of sealing ~by marking test
(see IS 5523
:
1983); and
Continuity of anodising coating, if required
(see IS 5523 : 1983).
In case of any change in raw material, manufacturing
method and operational conditions, all the tests as
given in this standard shall be carried out.
9 THICKNESS
9.1 Anodic oxide coatings are graded by their
thickness and are denoted by the grade numbers shown
in Table 1. The thickness of anodic coatings shall
not be less than specified in Table 1 for the appropriate
grade.
2
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9.2 Measurement of Thickness
in IS 5523
:
1983.
Thic-kness measurements shall be carried out by one
or more of the following methods:
a)
Microsection method,
b) Stripping method, and
c) Eddy current method (see IS 6012:1992).
10.2.3 For severe service (for example outdoors),
adequacy of sealing shall be tested by the sulphur
dioxide humidity test as specified in IS 5523
:
1983.
11 APPEARANCE AND COLOUR
9.2.1 In case of dispute, the Microsection method
shall be the referee method for coatings Grade AC
1.5 and higher thicknesses and stripping method shall
be used for thinner coatings (Grade AC 10, AC 5,
AC 2.5) and for coatings on wire.
9.2.2 Thickness measurements shail be made on the
significant surfaces and sharp edges should be avoided,
but no measurements shall be made within 5 mm
of the areas of anodic contact, nor in the immediate
neighbourhood of an edge.
11.1
Anodized articles shall be free from visible
defects on the significant surface(s) when viewed
from an agreed distance. If important to be customer,
the position and maximum size(s) of the contact
mark(s) shall be agreed between the anodizer and
the customer.
10 QUALITY OF SEALING
10.1 General
The quality of sealing is of great importance and
sealing is always essential, whether stated or not,
except where an unsealed coating is expressly
requested.
11.2
The colour, surface texture, and their
tolerances, shall be agreed between the anodizer
and the customer. If required for matching purposes,
the acceptable limits of variation shall be defined
by agreed samples.
The surface of anodized aluminium has the property
of double reflection from the surface of the base
metal. Therefore, when matching colour samples,
they shall be held in the same plane and viewed as
near to normal as is practicable, the direction of
working being always the same. A diffuse source
of illumination shall be placed behind the viewer.
10.2 Assessment of Qutility of Sealing
10.2.1
If test pieces are submitted, these shall measure
not less than 75 x 50 mm (see 8.1).
11.3 Unless otherwise agreed, the colours shall be
compared in diffuse daylight from a northern aspect
north of the equator and from a southern aspect south
of equator.
10.2.2 For mild environments (for example indoors),
sealing shall be tested by the marking test as given
If the coloured coatings are to be used in the service
in artificial light, this lighting shall bc used for colour
comparison.
IS
1868
:
1996
Table 1 Minimum Thickness of Anodic Coating
Cluuse 9. I)
;; lxle
I 1
A 25
Minimum Local
Thickness in
Micrometer
(3)
20
Applicution
(4)
For permanent installations, out doors and where little or no
deterioration ofsurface appearance are tolerated.evcn with mmimtnn
maintenance.
AC-15
A -Io
15
12
IO
8
For outdoor architectural rise, for indoor applications in
arduous conditions and for graphic application used for
defence XTVKCSand professional equipment.
May be used or outdoor in special applicationa whcrc
cleaning&very frequent(forexam~~le, dccora~lve rim for vehicles) and
also for cel-cain other indoor pplic tions like refrigerator parts.
5
4
Generally used for indoor applications
23
2
For some reflectors and as a base for paint.
NOTES
1 All grades may be produced in electrolytes based primarily on sulphuric or oxalic acid. With most chromic acid elelctrolytes.
only thinner coatings are obtainable. Barrier layer anodic coatings used in capacitors as dielectrics produced in boric acid electrolytes
are not included in the table.
2 For control purposes, thickness may be determined by addy current method or by breakdown voltage test.
3 Minimum Average thickness shall be the average of five measurements as specified in IS 5523
:
I993
3
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IS 1868 : 1996
11.4 The agreed colour samples shall be stored in
a dry place in the dark.
11.5 Standard colour panels as supplied by the user
may be used for acceptance of processed colour parts
subject to agreement between the manufacturer and
the purchaser. Colour matching shall, be carried out
by the day light in a room with northern aspect. The
agreed sample colour penels are to be stored in a
dark and dry place.
12 CORROSION RESISTANCE
If required by the customer, the anodic oxide coating
shall be tested for resistance to corrosion by, for
example, the AAS test as given in IS 6910 : 1985
or the CASS test as given in IS 5528
:
1985. The
choice of method and period of exposure shall be
as agreed to between the anodizer and the customer.
13 ABRASION RESISTANCE
If required by the customer, the abrasion resistance
of the anodic oxide coating shall be tested using a
method as agreed between the anodizer and the
customer. The performance requirements shall be
agreed ~between the anodizer and the customer in
accordance with the relevant provisions of IS
5523 : 1983.
14 RESISTANCE TO CRAZING BY
DEFORMATION
If required by the customer, the resistance to crazing
by deformation of the anodic oxide coating shall be
tested in accordance with the relevant provisions of
IS 5523 : 1983 and/or the performance requirements
shall be as agreed to between the anodizer and the
costomer.
15
FASTNESS TO LIGHT
15.1 General
For evaluating exterior colour fastness, only outdoor
exposure under conditions comparable to actual
service USC is acceptable. Accelerated testing is
suitable only as a quality control test of coloured
anodic oxide coatings where the. fastness of the
colouring medium has already been established by
outdoor exposure tests.
The light fastness of colour anodized aluminium
depends upon the method of colouring and the
colouring medium used, and only a limited range of
coloured finishes may be suitable in any particular
application. Advise in this regard should be sought
from the anodizer.
15.2 Fastness to Light
An accelerated method of testing the fastness of
coloured anodic oxide coatings to light is specified
in IS 5523 : 1983. When tested, the performance of
colour anodized aluminium in terms of Fastness rating
number shall be:
a) 5 Mire for interior application.
b) 9 Min for exterior application.
16 -LIGHT REFLECTION PROPERTIES
16.1 General
The following characteristic properties may be
measured:
a) Total reflectance (or total retlectivity)
b) Specular reflectance for surfaces with high
gloss
- at 45
-
at 30
-
at 20
c) Specular reflectance for surface with medium
or low gloss
-
at 60
- at 85
-
at 45
d) Diffused reflectance
These properties can be determined using a variety
of optical instruments, which differ in degree of
sophistication, cost and the type of surface for which
they are designed. These differences relate to the
illumination system, the angle of the incident light,
the angle at which the reflected light is measured
and the geometry of the light collecting system. The
properties are not, therefore, completely independent
of the instrument used for measurement.
Several of the properties require the provision of very
flat surfaces and measurements can only be carried
out on special test pieces.
The customer, wherever necessary, shall inform the
anodizer of the properties to be measured. They shall
also agree upon on the instrument as well as the
method of testing.
Bright finishes with a high specular gloss can however
be obtained only by the use of special grades of
aluminium.
17 ELECTRICAL BREAKDOWN POTENTIAL
If required, the electrical breakdown potential of the
anodic oxide coating shall be determined by the
method specified in IS 69 0 : 1985. The acceptable
breakdown potential shall, however, be agreed
between the anodizer and the customer.
18
CONTINUITY OF THE ANODIZE
COATINGS
If required, the continuity of the anodic oxide
coating shall be determined by the method specified
in IS 8375
:
1877. This test shall, however, be
applicable only to coatings of thickness less than 5
micrometer. The requirements for continuity shall,
however, be as agreed to between the anodizer and
the customer.
19 MARKING
The anodized articles shall be marked legibly and
indelibly with grade of the coating and the name or
trade-mark of the manufacturer.
4
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IS 1868 : 1996
IS
No.
1387 : 1993
Title
General requirements for the supply
of metallurgical materials second
revision)
IS No.
2500
Sampling inspection tables: Part
1
(Part 1)
:
1992
Attribute sampling plans indexed 6012: 1992
by acceptable quality level (AQL)
for lot-by-lot inspection second
revision) 665 1: 1972
ANNEX ,A
Clause 2)
LIST OF REFERRED INDIAN STANDARDS
3554
:
1966
Glossary of terms relating to
electroplating
6910:1985
5523
:
1983
Method of testing anodic coating
on aluminium and its alloys first
revision)
Method of testing corrosion
resistance of electroplated and
anodized aluminium coatings by
acetic acid salt spray (AAS) test
first revision)
5528
:
1985
Method of testing corrosion 8375: 1977
Method for checking continuity of
resistance of electroplated and
anodized coatings
ANNEX B
Clause 5)
B-l GENERAL
Aluminium, in most of its forms can be anodized
(see B-S), but the results differ widely in appearance,
colour, maximum possible coating thickness,
reflectivity, abrasion resistance, corrosion resistance
and electrical breakdown potential. The protective
value of the coating is excellent on aluminium
produced for general engineering purposes, but for
uniformity of appearance or other special effects
(for example bright finishes) special grades of
aluminium have been produced where close control
of chemical composition and metallurgical properties
are combined with special production procedures to
provide high standards of surface finish and a
guaranteed response to anodizing. These grades
cannot readily be classified because different
companies have developed their own range of
products to meet the requirements of a particular
industry or a customer and there is no clear dividing
line between the various categories.
The categories of coatings as listed below are given
for general guidance and are based on the end-use.
The anodizer must be therefore be aware of the end-
use, and it is stressed that, for this reason, there must
be close co-operation between the supplier of the
aluminium. the customer and the anodizer.
Title
anodized aluminium coating by
copper accelerated acetic acid salt
spray (CASS) test first revision)
Method for measurement of coating
thickness by eddy current
Anodized aluminium for
automobile use
B-2 ARCHITECTURAL QUALITY
Semi-finished products of this grade will give a
substantially uniform appearance after anodizing when
viewed from a distance of not less than 3 m.
Some variations in appearance and colour can be
expected after anodizing, between different batches
of the same material and between different forms oJ
the same material. It is sometimes possible to observe
on close inspection, or from certain viewing angles,
variations in brightness, banding, streaking and other
visual defects. These do not affect in any way the
quality of the coating. The extent to which such defects
can he accepted shall be specified by the costomer.
Special alloys have been developed for use with
integral colour anodizing processes and these may
have to bc specified for particular coloured finishes.
B-3 DECORATIVE QUALITY
Semi-finished products of this catcqory have a
particularly homegeneous
nppearancc when viewed
from a distance of 0.5 m. The finish may be matt,
bright or semibright according to the material and
anodizing treatment, but freedom from defects is
assured (see
11 .
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IS 1868 : 1996
B-4 BRIGHT ANODISING QUALITY
Materials in this category will normally be based on
ingot metal aluminium of high (99.7 percent) or very
high (99.99 percent) purity. Proper manufacturing
control of the metal is essential.
B-5 GENERAL ENGINEERING QUALITY
Most aluminium will come within this category and
will anodize to give a continuous coating of good
IS 1868: 1996
protective value but with no guarantee about
appearance, although it may be good.
Alloys containing high proportions of copper, silicon
or zinc are likely to create, problem in anodizing
and advise should be sought from the manufacturer
and the anodizer, in particular, if the copper content
is higher than 3 percent since anodising as _it will
offer only a limited protection.
NOTE - IS 66.51:1972 may be referred for requirements
of anodized aluminium for automibile use.
ANNEX C
Clause )
C-l The pretreatment given before anodizing
largely determines the final appearance and texture
of the anodized aluminium surface. Different surface
texture may be obtained by a variety of treatment
processes.
The work may be mechanically polished to obtain
a smooth or bright surface. Chemical or
electrochemical brightening can also be
employed with special aluminium to obtain a
very bright finish.
Usually, the work, either polished or unpolished, is
subjected to a chemical etching procedure to provide
a range of texture from light satin with varying degrees
of gloss to full matt, depending upon the type of
etch used.
Alternatively, the texture may be produced
_mechanically using brushes, abrasive belts or wheels
to give matt finishes which are lined or directional
in contrast to the essentially non-directional etched
finishes. Mechanical finishes have good
reproducibility and are less dependent on metal
structure and composition than chemical pretreatment
finishes. Surface irregularities, if not too deep, can
also be removed by mechanical means.
C-2 The desired surface texture shall be agreed
between the anodizer and the customer and, if
necessary, on the basis of agreed samples. The
provision of such samples is a useful guide in
production, but it should be recognized that they are
of limited value in assessing surface finish, since
different forms and sizes of matcrinl may respond
to pretreatments in slightly different ways.
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lhreau of Indian Standards
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without the prior permission in writing of BIS. This does not preclude the free use, in the
course of
implementing the standard, of necessary details, such as symbols and sizes, type or grade designations.
Enquiries relating to copyright be addressed to the Director (Publications), BIS.
Review of Indian Standards
Amcndmcnts are issued to standards as the need arises on the basis of comments. Standards are also
rcvicwcd periodically; a standard along with amendments is reaffirmed when such review indicates that
no changes are needed; if the review indicates that changes are needed, it is taken up for revision. Users
of Indian Standards should ascertain that they are in possession of the latest amendments or edition by
referring to the latest issue of BIS Handbook and Standards Monthly Additions.
This Indian Standard has been developed from Dot : No. MTD 20 (4076).
Amendments Issued Since Publication
Amend No. Date of Issue Text Affected
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